explain reasons for controlling invasive alien species

Conservation – Biodiversity, Threats & Control of Invasive Alien Species (Cambridge International AS & A‑Level Biology 9700 – Topic 18)

1. Biodiversity – Definition and Measurement

• Genetic diversity – variation of alleles within and between populations.

  • Typical measures: heterozygosity (H), % polymorphic loci, allelic richness.

• Species diversity – number of species (species‑richness) and their relative abundances.

  • Common indices:

    Index	Formula (simplified)	Interpretation
    Simpson’s Index (D)	∑ pi²	Higher D = lower diversity (probability two random individuals belong to same species).
    Shannon‑Wiener Index (H′)	−∑ pi ln pi	Higher H′ = higher diversity (accounts for richness & evenness).

• Ecosystem diversity – variety of habitats, biotic communities and ecological processes within a region (e.g., forests, wetlands, coral reefs, peatlands).

2. Classification – Why It Matters for Conservation

3. Six Principal Threats to Biodiversity

4. Conservation Strategies

4.1 In‑situ Conservation

• Protected areas – National parks, nature reserves, Marine Protected Areas (MPAs).
• Habitat restoration – Re‑forestation, wetland creation, removal of barriers, re‑connection of habitat corridors.
• Legislative protection – Wildlife Acts, species‑specific orders, bans on trade.
• Community‑based management – Sustainable use schemes, ecotourism incentives, Indigenous stewardship.

4.2 Ex‑situ Conservation

• Seed and gene banks – Preserve genetic material for future re‑introduction.
• Captive breeding programmes – Zoos, aquaria, livestock breeding for critically endangered species.
• Botanical gardens & arboreta – Safeguard rare plant taxa and provide material for restoration.

4.3 Integrated Conservation

Combines in‑situ and ex‑situ actions, underpinned by monitoring, research, and public education. Adaptive management adjusts actions as new data become available.

5. International Conventions & National Legislation

6. Genetic Conservation – Why Genetic Diversity Matters

• Supplies raw material for adaptation to changing environments (e.g., climate change, emerging diseases).
• Reduces inbreeding depression, which can lower reproductive success and increase disease susceptibility.
• Essential for the long‑term viability of small or isolated populations – a key consideration when planning re‑introductions.
• Preserved through gene banks, cryopreservation, and managed breeding programmes.

7. Reasons for Controlling Invasive Alien Species (IAS)

Control is justified on ecological, economic, health, legal and ethical grounds. Early action is usually the most cost‑effective.

• Preserve native biodiversity – Prevent extinction or decline of indigenous species.
• Maintain ecosystem function – Safeguard pollination, nutrient cycling, soil stability, and trophic interactions.
• Protect economic interests – Avoid losses in agriculture, fisheries, forestry, horticulture and tourism.
• Reduce health risks – Limit disease vectors (e.g., mosquitoes, rats) and toxic or allergenic plants.
• Comply with legal & ethical obligations – National wildlife acts, CBD commitments, precautionary principle.
• Prevent irreversible changes – Early eradication is cheaper and more successful than long‑term management.

8. Evaluation of Control Methods

9. Integrated Management Cycle for IAS

1. Prevention – Quarantine, border inspections, risk‑assessment of pathways, public awareness campaigns.
2. Early Detection & Rapid Response (EDRR) – Regular monitoring, citizen‑science reporting, rapid eradication when populations are small.
3. Long‑term Management – Combination of mechanical, chemical, biological, and habitat‑based methods; adaptive management informed by monitoring data.
4. Evaluation & Review – Cost‑benefit analysis, ecological impact assessment, revision of objectives and methods.

10. Case Study – American Mink (Neovison vison) in the United Kingdom

• Pathway of introduction – Escape from fur farms (mid‑20th century) and deliberate releases.
• Ecological impacts

  • Predation on water voles (Arvicola amphibius), ground‑nesting birds (e.g., red‑breasted merganser), amphibians and small fish.
  • Competition with native mustelids such as the European polecat (Mustela putorius).
  • Potential disease transmission (e.g., Aleutian disease virus).

• Control measures

  • Targeted live‑trapping programmes (e.g., “Mink Trapping Initiative”).
  • Habitat enhancement for water voles – riparian vegetation planting, flow regulation, predator‑exclusion fencing.
  • Public reporting hotlines and citizen‑science apps to aid EDRR.

• Outcomes (2015‑2020)

  • Average 40 % reduction in mink density in targeted river catchments.
  • Water‑vole occupancy rose from ~30 % to ~68 % of historic sites.
  • Demonstrates the importance of integrating mechanical removal with habitat restoration.

11. Summary – Key Points for A‑Level Exams

• Understand the three levels of biodiversity (genetic, species, ecosystem) and how they are measured.
• Know the three classification systems and why they matter for conservation planning.
• Recall the six principal threats, with invasive alien species as a major, manageable threat.
• Distinguish in‑situ, ex‑situ and integrated conservation approaches and give concrete examples.
• Identify the main international conventions and national legislation that support biodiversity protection.
• Explain why genetic diversity is essential for long‑term species survival.
• List the ecological, economic, health, legal and ethical reasons for controlling IAS, and recognise that early action is most cost‑effective.
• Be able to evaluate the advantages, disadvantages and feasibility of the main control methods.
• Describe the four‑stage IAS management cycle and apply it to a real case (e.g., American mink).